Download (direct link):
<svg width="5cm" height="3cm" viewBox="0 0 5 3" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<desc>Example link01 - a link on an ellipse</desc>
<rect x=".01" y=".01" width="4.98" height="2.98"
fill="none" stroke="blue" stroke-width=".03"/>
<ellipse cx="2.5" cy="1.5" rx="2" ry="1" fill="red" />
Listing 6.11 Simple SVG example.
Listing 6.11, an example taken from the SVG Recommendation of the W3C, creates an image of a red ellipse, shown in Figure 6.7. When a user clicks on the ellipse, the user is taken to the W3C Web site. Of course, this is one of the simplest examples. SVG takes advantage of XLink for linking.
Figure 6.7 Rendering a simple SVG file.
If product adoption is any indicator, the SVG specification is quite successful. In a very short time, vendors have jumped on the SVG bandwagon. The Adobe SVG Viewer, the Apache Batik project, the SVG-enabled Mozilla browser, the W3C's Amaya editor/browser, and Jasc's WebDraw application support SVG, to name a few. Some are SVG renderers, and some projects generate SVG content on the server side. Because it is natively XML, Web services can generate rich graphical content. SVG is an important technology that can be a part of a service-oriented Web.
This chapter has provided a very brief tour of some very important XML technologies. Because the purpose of this chapter was to provide a big picture of some of the key technologies, Table 6.1 presents a reference of some of the key issues.
Understanding the Rest of the Alphabet Soup
Table 6.1 Summary of Technologies in This Chapter
STANDARD DESCRIPTION W3C STATUS KEY RELATED TECHNOLOGIES
XPath Standard addressing mechanism for XML nodes XPath 1.0— Recommendation; XPath 2.0—Working Draft Almost every XML technology uses it, notably XSLT, XPointer, XLink, XInclude, XQuery.
The Stylesheet Used for Languages transforming and (XSLT/XSL/ formatting XML XSLFO) documents XSL 1.0— Recommendation; XSLT 1.0— Recommendation; XSLT 2.0—Working Draft XPath provides an addressing basis for XSLT.
XQuery Querying mechanism for XML data stores (“The SQL for XML") XQuery 1.0— Working Draft XQuery and XPath share the same data model.
XLink General, all-purpose linking specification XLink 1.0— Recommendation SVG uses it; XLink can use XPointer.
XPointer Used to address nodes, ranges, and points in local and remote XML documents XPointer framework, xpointer() scheme, xmlns() scheme, and element() scheme — All Working Drafts XPath provides an addressing basis. Can be used in XLink, XInclude.
XInclude Used to include several external documents into a large document XInclude 1.0— Candidate Recommendation N/A
XML Base Mechanism for easily resolving relative URIs W3C Recommendation N/A
XHTML A valid and well-formed version of HTML, with noted improvements XHTML 1.0— Recommendation; XHTML 2.0— Working Draft HTML
XForms A powerful XML-based form-processing mechanism for the next-generation Web XForms 1.0— Candidate Recommendation Uses XPath for addressing
SVG XML-based rich-content graphic rendering SVG 1.0— Recommendation Uses XLink
All the technologies in Table 6.1 have a future. However, they are all evolving. Of the standards we've discussed, XPath, XSLT/XSL, XHTML, and SVG seem to have the most support and adoption. However, they all achieve important goals, and as the influence of XML grows, so will support. For more information on these standards, visit the W3C's Technical Reports page at http:// www.w3.org/TR/.
'The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in cooperation."
—Tim Berners-Lee, James Hendler, Ora Lassila, "The Semantic Web," Scientific American, May 2001
The first step toward a Semantic Web and using Web services is expressing a taxonomy in machine-usable form. But what's a taxonomy? Is it related to a schema? Is a taxonomy something like a thesaurus? Is it a controlled vocabulary? Is it different from an ontology? What do these concepts have to do with the Semantic Web and Web services? What should you know about these concepts?
This chapter attempts to answer these questions by discussing what a taxonomy is and isn't. Some example taxonomies are depicted and described. Taxonomies are also compared to some of the preceding concepts using the framework of the Ontology Spectrum as a way of relating the various information models in terms of increasing semantic richness. Because a language for representing taxonomies is necessary, especially if the taxonomy is to be used on the Web, for Web services, or other content, this chapter will also introduce a Web language standard that enables you to define machine-usable taxonomies. Topic Maps is then compared with RDF (introduced in Chapter 5). This chapter concludes with a look ahead to Chapter 8 and ontologies.